Cause of 1952 deadly London fog determined

When you think of London you probably imagine some fog resting over the city.

For an outsider it seems like a charming adjective to a great city, however that wasn't always the case.

In 1952, a fog settled over the city for five days in December.

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The Battle of Cable Street: London immigrants fight fascist march

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The Battle of Cable Street: London immigrants fight fascist march

4th October 1936: British politician Sir Oswald Ernald Mosley (1896 - 1980) inspects members of his British Union of Fascists in Royal Mint Street, London. The photograper Len Puttnam is seen left. The BUF's presence sparked a riot which became known as the Battle of Cable Street. (Photo by Central Press/Getty Images)

4th October 1936: British politician Sir Oswald Ernald Mosley (1896 - 1980) inspects members of his British Union of Fascists in Royal Mint Street, London. Their presence sparked a riot which became known as the Battle of Cable Street. (Photo by Central Press/Getty Images)

(GERMANY OUT) Riots between anti-Fascists and Blackshirts (British Fascists) when Mosley's supporters were gathering in Great Mint Street for a march through the East End of London in what is now called the Battle of Cable Street; anti-Fascists are pushed back by police on October 4, 1936 (Photo by ullstein bild/ullstein bild via Getty Images)

(GERMANY OUT) Riots between anti-Fascists and Blackshirts (British Fascists) in London: anti-Fascists were setting up barricades against a march of Mosley's supporters in Cable Street in the East End of London in what is now called the Battle of Cable Street; police removing the barricades on October 4, 1936 (Photo by ullstein bild/ullstein bild via Getty Images)

4th October 1936: Policemen arresting a demonstrator when fascists and communists clashed during a march know as the Battle of Cable Street led by British fascist Sir Oswald Mosley in London's East End. (Photo by Topical Press Agency/Getty Images)

'Battle of Cable Street', Aldgate, London, 5th October 1936. An anti-Fascist crowd, some of them carrying missiles, run from a barricade they have erected near Aldgate. The police are charging on the far side of the barricade, which has been reinforced with paving stones. (Photo by Jewish Chronicle/Heritage Images/Getty Images)

(GERMANY OUT) Riots between anti-Fascists and Blackshirts (British Fascists) in London: anti-Fascists were setting up barricades against a march of Mosley's supporters in Cable Street in the East End of London in what is now called the Battle of Cable Street; an anti-Fascist is taken away by police on October 4, 1936 (Photo by ullstein bild/ullstein bild via Getty Images)

(GERMANY OUT) Riots between anti-Fascists and Blackshirts (British Fascists) in London: anti-Fascists were setting up barricades against a march of Mosley's supporters in Cable Street in the East End of London in what is now called the Battle of Cable Street; an anti-Fascist is taken away by police on October 4, 1936 (Photo by ullstein bild/ullstein bild via Getty Images)

5th October 1936: Repairing a pavement in Cable Street, Mark Lane, London which was ripped up to prevent a Fascist march. (Photo by Maeers/Fox Photos/Getty Images)

(GERMANY OUT) Riots between anti-Fascists and Blackshirts (British Fascists) when Mosley's supporters were gathering in Great Mint Street for a march through the East End of London culminating in the Battle of Cable Street; an activist who lost her shoe is taken away by police (Photo by ullstein bild/ullstein bild via Getty Images)

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When it finally went away, there were more than 150,000 people hospitalized and more than 4,000 people dead.

The fog was toxic, but the specifics of how or why it was toxic weren't fully understood until now.

Scientists from the U.K., U.S. and China looked into the matter in the hopes of preventing another such event.

The results of the study point the finger at coal burning. The lead researcher said sulfur dioxide, which is a byproduct of coal burning, was turned into sulfuric acid in the fog when it got trapped.

This was apparently happening because nitrogen dioxide, another by-product of coal burning, also got trapped in the fog facilitating the deadlychemical transition.

When the fog lifted, it left an acidic haze over the city.

This is scary in places like China where coal burning is still the norm. Hopefully this new research will lead to changes before we witness another tragedy.